(1) Field of the Invention
This invention relates to dye dispersants. More particularly, this invention relates to a dispersing composition containing sulfonated lignin and an aromatic sulfonic acid.
(2) The Prior Art
Dyestuff compositions typically comprise a dye cake, i.e., of disperse dyes or vat dyes, and a dispersant. These types of dyestuff compositions are widely used to color both natural and synthetic fibers. In the dyestuff composition, the dispersant serves three basic functions: It assists in reducing the dye particle to a fine size; it maintains a dispersing medium; and it is used as a diluent. Dye dispersants are generally one of two major types, sulfonated lignins from the wood pulping industry or naphthalene sulfonates from the petroleum industry.
The disadvantages of lignins, whether they are sulfite lignins or sulfonated kraft lignins, include fiber staining, reduction of diazo-type dyes, dark brown color and a tendency to stabilize foams. These adverse properties are bothersome to the dyers. Many attempts have been made to modify lignins to overcome their inherent disadvantages. The most common approach to alleviate fiber staining has been to reduce the adsorptive functionality of the lignin over chemical reaction pathways, such as, for example, total or partial blocking of phenolic hydroxyl units. Exemplary of lignin modification for these purposes is set forth in U.S. Pat. No. 3,841,887 to Falkehag et al.
Fiber staining by the lignin occurs mainly on cellulosic and nitrogenous fibers, such as cotton, nylon and wool; polyester fibers are also stained but to a lesser extent. The brown stain tends to impart a dull appearance to the dyed fiber which is undesirable. Moreover, the brown lignin stain tends to fade upon exposure to sunlight.
The disadvantages of naphthalene sulfonates include heat stability and little dye retarding properties. On the other hand, an advantage of lignin dispersant is that it tends to act as a dye retarder. Some dyes have a tendency to start dyeing at very low temperatures. Dyers prefer colors to dye a fiber at a steady rate proportional to temperature increase. If the color dyes too rapidly, the goods take on a streaky appearance; and creases in the material dye more rapidly than the face of the cloth.
With the advantages and disadvantages of various types of dispersants in mind, it is, therefore, the general object of this invention to provide a dye cake dispersant containing a mixture of a sulfonated lignin and an aromatic sulfonic acid that is capable of reducing dye particles to a fine size, satisfactorily dispersing the dye, and substantially reducing fiber staining.
Another object of this invention is to provide a lignin-containing dye dispersing composition having the desired properties that does not require expensive modification of the lignin.
Still another object of this invention is to provide dye dispersing compositions containing sulfonated lignin having a low viscosity.
Yet another object of this invention is to provide dye dispersing compositions containing sulfonated lignins that are heat stable.
Other objects, features and advantages of the invention will be evident from the following detailed description.